As the title says. I want to be 100% sure rather than test and not notice some hard to spot bug 
Yes, Octopack(ages) are compatible across versions.
Some differences in Powershell execution can cause problems, so re-testing in a non-critical environment is recommended.
Are the powershell changes documented somewhere or could you explain? Thanks!
Hi Ryan, we have some details here: https://github.com/OctopusDeploy/Issues/wiki/Migrating-from-Octopus-Deploy-1.x#variables
Using the most recent version of the migrator should fix these up automatically. The list should be “99%” complete, if you hit any trouble please let us know.